Animal Nutrition/Digestion

Chapter 41 & IB Topic 6.1

Introduction Physiology: how and why the parts of the

body function the way they do Anatomy: the study of the structure.

Structure and function Physiology is an experimental science

Cells of organisms function best in a constant internal environment

Digestion The body needs to get essential nutrients An essential step because the bulk of food

taken in consists of insoluble molecules Too large to cross the gut wall and enter the

blood stream The bulk of our diet consists of:

carbohydrates, lipids, and proteins Must be hydrolyzed Food cannot be said to have truly entered the

body until it has been digested and absorbed

The five steps of nutrition 1. Ingestion 2. Digestion 3. Absorption 4. Assimilation 5. Egestion/elimination

Ingestion Food is taken into the mouth for

processing in the gut

Digestion Process of breaking food down into

molecules small enough for the body to absorb

Mechanical digestion Teeth (mastication) and muscular walls of the

gut (peristalsis: waves of contraction and relaxation

Increases surface area Chemical digestion

Enzymes (mainly in the stomach and intestine)

Absorption Soluble products of digestion are absorbed

into blood circulation system

Assimilation Products of digestion absorbed from blood

into body cells (such as liver and muscle cells) and used or stored

Egestion or elimination Undigested food and dead cells from the

lining of the gut, together with bacteria from the gut flora, expelled from the body as feces

Enzymes (remember … ) Huge contributor in chemical digestion Digestion enzymes are protein catalysts

produced in specialized cells in glands associated with the gut

Enzymes speed up the breakdown of insoluble food substances

Remember pH and temperature Think homeostasis

What you need to know: Enzyme Source Substrate Product Optimum

pH

Amylase Salivary glands

Starch Maltose 6.5-7.5

Pepsin Gastric glands

Protein Polypeptides 2.0

Lipase Pancreas Triglyceride Fatty acids and

glycerol

7.0

Lets take a trip down the alimentary canal … 1. The oral cavity 2. The stomach 3. The small intestine 4. The large intestine

Also reference Figure41.13 in your text

The oral cavity Mechanical and chemical manipulation of food Saliva moistens food and helps prevent tooth

decay by buffering/neutralizing acids Also contains antibacterial agents

The pharynx Opens both to the windpipe (trachea) and esophagus When we swallow, the windpipe moves up and the

glottis is covered by the epiglottis The esophagus

Food travels down the esophagus to the stomach Peristalsis

The stomach J-shaped, pouch-like organ that hangs

inferior to the diaphragm in the upper left portion of the abdominal cavity

1-2 L capacity The wall of the stomach is elastic, so large

meals can be swallowed quickly, stored, and then gradually released into the small intestine

The wall of the stomach is muscular and contracts rhythmically to squeeze the food, mixing it and breaking it into smaller lumps

Functions of the stomach Gastric glands secrete gastric juices

(includes HCL) HCL has a pH of 1.5-2.0 Good for protein digestion (protease)

Goblet cells secrete mucus Prevents autolysis

Chyme Semi-liquid

A typical meal may spend up to 4 hours in the stomach

The small intestine Completion of digestion of carbohydrates,

lipids, and proteins Useful products are absorbed In humans, about 5 meters long The inner-most layer contains finger-like

projections called villi

Digestion in the small intestine Food enters the first part (duodenum) a

little at a time The chyme meets bile from the bile duct

and the pancreatic juice from the pancreas Bile neutralizes the acidity of the chyme Bile lowers the surface tension of large fat

globules (emulsification) Pancreatic juice contains several enzymes:

amylase, lipase, and protease

Absorption in the small intestine The products of digestion (monomers,

minerals, vitamins) are absorbed as they make contact with the villi

Efficient because the villi drastically increase the surface area of the small intestine

Active transport Products of digestion are taken into cells Protein pump molecules

Assimilation follows absorption The fate of absorbed nutrients is called

assimilation In the villi:

Sugars are passed into the capillary network, then to the liver

Amino acids are passed into the capillary network, then to the liver (make new proteins)

Lipids are absorbed as fatty acids and glycerol into the lacteal vessels lymphatic system blood circulation

The large intestine No villi; surface area is increased by numerous

folds At this point, most of the useful nutrients have

been absorbed What remains:

Undigested matter (plant fiber), mucus, dead intestinal cells, bacteria, mineral ions, and water

In the colon, water and mineral salts (Na+, Cl-) are absorbed

What remains is now called feces Bacteria compose about 50% of feces (so wash your

hands!) Bile pigments color the feces

Animations http://www.pennhealth.com/health_info/an

imationplayer/ Digestion Peristalsis Heartburn Ulcers

Lets Model A Trip Down the Alimentary Canal … Students will be assigned a portion of the

digestive system Arrange yourselves in the proper order Pink Koosh ball will represent a piece of food As the “food” passes from person to person down

the digestive system, the student who is holding the ball will state the function of their body part in processing the food. In some cases, the food may not reach you – you are a

vital, accessory organ

Small Group Discussion What would be the consequences if a person’s stomach was

surgically removed, or did not function properly? What about:

Small intestine Large intestine Pancreas Gall bladder Liver Teeth and/or tongue Salivary glands

Which of these digestive organs could you live without? What accommodations would you need to make to maintain good nutrition and digestive function? Which of these organs are absolutely impossible to live without?